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VAMSI DANDA

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Electronics hobbyists enjoy playing with the projects.some people start a garage at home. For making any new invention you don't need any big laboratory. you can make your home a LAB.to work you just need a "multimeter". I have been working on some projects.At the beginning stage i made so many disasters in my room.I blasted so many components(one day i burnt my bed).what ever we do we enjoy that.So i just wanted to share some of my work with you.

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Thursday, 2 August 2012

If you want to make your robot sense the objects in it's surroundings i suggest you to go for an ULTRASONIC sensor.Though the IR based sensors are cheep, their working range may vary due change in ambient light and won't give accurate range values.

In case of ULTRASONIC sensors they work based on the principle of RADAR(RAdio Detection And Ranging). A RADAR transmits electromagnetic "pulse" towards the target and receives the "echo" reflected by the target.

Then the range of the target is determined by the "time lagging" between transmitted pulse and the received "echo". Generally microwave and ultrasonic frequencies are used in RADARS

Our HC-SR04 ultrasonic sensor works similar to the RADAR mechanism but in a simplified manner. This sensor consists of four PINS

1.Vcc------------------connect to 5V dc

2.Trigger--------------pulse input that triggers the sensor

3.Echo----------------indicates the reception of echo from the target

4.Gnd-----------------ground final

working with sensor step by step

Take a look at the timing diagram of HC-SR04 sensor

This diagram describes the basic algorithm in distance measuring using the sensor.

STEP1.Make
"Trig" pin of the sensor high for 10µs. This initiates a sensor cycle.

STEP2.8 x 40 kHz pulses will be sent from
the transmitting piezzo transducer of the sensor, after which
time the "Echo" pin on the sensor will go from low to high.

STEP3.The
40 kHz sound wave will bounce off the nearest object and return to the sensor.

STEP5. The
distance between the sensor and the detected object can be calculated based on
the length of time the Echo pin is high.

STEP6.If
no object is detected, the Echo pin will stay high for 38ms and then go low.

configuring the 8051 microcontroller:

To inter face the sensor to AT89S51 microcontroller we need two I/O pins. One of them is external interrupt pin(INT0 or INT1) for measuring the pulse width at the echo pin. and any other pin say P3.5 for trigger.

STEP1.Connect the trigger pin of
sensor to P3.5 of AT89S51

STEP2.Connect the echo pin of the
sensor to INT0 (P3.2) of AT89S51

STEP3.Configure the TIMER0 of
8051 in 16 bit mode with “GATE” bit enabled. If the GATE pin is enabled and
timer run control bit TR0 is set, the TIMER0 will be controlled by INT0 pin.
When INT0 is high then the TIMER0 starts counting. Whenever INT0 goes low TIMER0
holds its count. So load the TMOD register with 00001010==0x0A; (better refer to
any book of 8051).

STEP4.As the INT0 pin is input don’t
forget to declare the pin input. Write “1” to the pin to make it input.

algorithm

==>Send a 10 micro second high
pulse at trigger

Initially P3.5=0;

P3.5=1;

Delay(10 micro second);

P3.5=0;

==> "WAIT" until the sensor transmits the eight 40KHz pulses and signal reflection. initially the "ECHO"pin is low when the transmitter completes the pulse the pin goes high then our TIMER0 starts counting.when input at INT0 goes low timer holds count. logic for waiting: while(INT0==0); while(INT0==1); but some times due to errors in the sensor functioning the 8051 microcontroller may go into an "INFINITE LOOP" for that there are two remedies1)use watch dog timer(present on AT89S52 and other advanced versions)2)generate a delay of 40 milliseconds after triggering the ultrasonic sensor.the second option is preferred for beginners. ==>TIMER0 value = time taken by the signal to (go forward+come back)It meas the signal traces the whole distance twice. so time taken by the signal to travel the distance = TIMER0 value/2 ULTRASONIC pulse travels with the speed of sound 340.29 m/s= 34029 cm/s range of target= velocity *time ==> 34029 * TIMER0/2 ==> 17015 * TIMER0At 12MHz TIMER0 gets incremented for 1microsecond. RANGE = 17015 centimeters/seconds * TIMER0 micro seconds

unsigned char get_range(void) { unsigned char range; send_pulse(); while(!INT0);// in sake of these lines you can generate a delay of 40 Milli seconds=40000 micro while (INT0);// seconds DPH=TH0;DPL=TL0; TH0=0xFF;TL0=0xFF; if(DPTR<35000)//actually you need to use 38000 but the sensor may not work at higher levels range=DPTR/59; else range=0; // indicates that there is no obstacle in front of the sensor return range; }void main(){//main begin TMOD=0x09;//timer0 in 16 bit mode with gate enable TR0=1;//timer0 run enabled TH0=0x00;TL0=0x00; P3|=0x04;//setting pin P3.2 to make it INPUT

unsigned int target_range=0; while(1) { target_range=get_range(); //make your own function to display the range value.better to use LCD }}// end of main